Heretofore intake manifold vacuum spoilers have been utilized in order to reduce the speed of air passing through the carburetor of an associated internal combustion engine and the vacuum at the outlet ends of at least some of the fuel passages of the carburetor to thereby increase the air-fuel ratio in order to provide more economical operation. In addition, prior attempts have been made to incorporate a vacuum spoiler within the positive crankcase ventilation systems of more recently designed vehicle internal combustion engines in order that the vacuum spoiler systems may be compatible with attempts to reduce combustion engine emissions.
However, most of these previous attempts have incorporated operational characteristics which either excessively increase the air-fuel ratio or do not provide a sufficient increase in air-fuel ratio when the associated internal combustion engine is operating at cruising speeds. It is important that an internal combustion engine be operated under reduced air-fuel ratios when operating at high speeds or under heavy loads in order to reduce the temperature of combustion within the engine and thus the tendency of the exhaust valves of the engine to burn.